Stepping up starter during fermentation

I've got some PacMan yeast a cultured from a Dead Guy bottle two days ago. It's going along well and it've got quite a bit of yeast in the bottle of a 2L growler. I'm wanting to step up the starter to get a larger quantity of yeast before I move it to the fridge to save for brewing. I'm past the initial yeast development phase and into or almost done with active fermentation. Can I step up the current 16oz. starter to a full 2L during active fermentation? Or should I wait till it's done fermenting, chill, decant the liquid, and then step it up after that?

A bunch of us are doing the same thing this week....

Prof Fink gives good advice here;

https://www.homebrewtalk.com/showthread.php?t=63855

I guess my question is there are three phases I can think of. Yeast growth and muliplication, then active fermentation, then completion where the yeast settle back down to the bottom. I've read about people stepping up during the growth phase as well as waiting till fermentation is done, and pitching into a larger body of wort, but can you pitch more wort while the yeast is actively fermenting in order to build up more yeast?

I'm in the same boat this week and wondering the same thing. Just add more wort? Or throw it in the fridge, decant the old stuff (lazy unsettled yeast) and add fresh wort? Trying to step up from 2 cups to 2L.

Im the starter of the Pacman yeast thread you guys were refered to. What I have been doing is just adding more wort to the situation. Once my 2L flask shows up Im going to fridge the yeast/wort combo I have now and then pour all the yeast into the 2L falsk and start over. I think once fermentables are added into the tired yeast they get active again and start to multiply.